Auto Service World
News   June 30, 2016   by Jeff Taylor

Adapting to speed and distance

Part 2 of 7 in an exclusive series

This is the second in a series of article on changing vehicle technologies – exclusive to the AutoServiceWorld Knowledge Centre. Award-winning tech writer Jeff Taylor offers a look at some of the latest innovations in the automotive world, how they work, how they’re evolving, and what they mean to the aftermarket.


Adaptive cruise control may sound complex… but because today’s vehicles are virtually all drive-by-wire, it’s probably not as complicated as you might think!

By Jeff Taylor

Adaptive cruise control (ACC), active cruise control (ACC), or intelligent cruise control (ICC) are just a few of the names being used to describe an additional vehicle feature that complements today’s cruise control.

Audi adaptive cruise control system

Audi adaptive cruise control system

With the use of a ‘headway sensor’ to detect vehicles on the road ahead, the ACC system not only maintains a vehicle’s speed – just as cruise control has always functioned in the past – but now offers the added benefit of maintaining a pre-set distance to the vehicle in front of it.

If the ACC system is paired with some form of collision-mitigation system (and they often are), it could activate the vehicle’s braking system.

Some systems that also allow for the wide range of speeds – from flying along to barely crawling – that are frequently encountered in stop-and-go commuter traffic.


Sounds complex? Well, it is… but because today’s vehicles are virtually all drive-by-wire, the integration of the ACC onto the vehicles system is not as complicated as you might think. Using the existing CAN network system for high-speed communications, the ACC will seamlessly communicate to the PCM for throttle control, cruise control status, brake system, and any other systems that may be used on a particular vehicle set-up.

What does the customer driver have to do?

To activate the ACC, the driver will set the cruise speed they wish to maintain. But in addition, they’ll have to specify a comfortable gap they’d like to maintain to the vehicle ahead of them. It might be measured in time (seconds of travel time) or the actual distance.

This is the active or adaptive part. Many systems will allow the driver to turn off the ACC and just have regular cruise control.

If there’s no traffic, the ACC system functions the exact same as a regular cruise system. But if the ACC system detects a vehicle going slower, it will ask the PCM to slow down, instigate a coast situation, or actually apply the brakes to maintain the pre-set distance.


Chrysler will allow up to 25% of the brakes to be applied but it’s different across manufacturers.

Partial ACC system are not able to fully apply the brakes – only enough to slow the vehicle down at a certain rate. But if the system detects that the vehicle is still closing too fast, there will be some form of driver alert to apply the brakes. This alert can be visual and audible.

Many newer vehicles now have the ability to come to a full stop to avoid a collision or a pedestrian that has stepped into the path of the vehicle. Some systems will actually accelerate the vehicle to perform an overtaking maneuver if it approaches a slower-moving vehicle when the left signal is activated.


Drivers may notice that they’re going slower than the speed they initially set, because the ACC has adapted to that speed. But once the path in front clears or the traffic thins out, the ACC should resume the speed that was initially set.

All systems will disengage when the brake pedal is applied just like regular cruise control system.

What makes this system work?

ACC depends on the system knowing what is in the lane in front of the vehicle. To gather this information, it employs a ‘headway sensor’ or a series of sensors. The headway sensor can take different forms: a laser, lidar, radar, or forward facing stereoscopic cameras (as used by Subaru and BMW). Many systems will use a combination of methods for detection and work day or night, but they can be affected by adverse weather conditions like heavy rain, snow or fog.


Radar is the most popular headway detector at the moment. It outperforms laser detection. Lasers can be confused by reflections and dirty sensors. Radars work better in most weather conditions. The radar units used for ACC employ microwave signals of different wave lengths; 24, 35 or 76 GHz are common and these won’t interfere with police radar. There are three areas that the radar units typically scan; short-range, mid-range, and long-range.

Short-range wide angle radar typically detects objects in an 80-degree angle scan pattern from 20cm to 30m distance. The wide angle is used to accurately detect against adjacent lane detection and pedestrians (collision mitigation). The medium-range scans a narrower area of about 60 degrees but reaches approximately 60m. Long-range detection works in a relatively narrow band of about 18 degrees at 200m, to give better resolution for a vehicle farther away.

The electronically scanning multi-mode radar sensor is a prevalent method being used for ACC. This type of radar simultaneously allows for long- and mid-range detection, and when used with a camera or short-range unit can have a range of about 20cm to 500m.


There are different versions of ACC and they will require different hardware and have different capabilities, the partial ACC system may only over a limited speed range (Nissan’s first ACC only worked from 5 to 100 km-h) or they may disengage when the speed drops below 25 km-h.

The partial system will not bring the vehicle to a full stop. These systems typically only had the multi-mode radar typically mounted behind the grill area of the vehicle.

The more complex systems involve two radar sensors (short-range and multi-mode for medium and long ranges) so that they can accurately detect closer objects for stop-and-go traffic situations. These systems will allow the vehicle to come to a complete stop, and then resume when traffic starts to flow again.

There are different safety features built in that may make the driver touch the resume button or tap the brakes so the system knows the driver is still pay attention, if they don’t do this interaction, the system will disengage.

So… what will see in the shop?

Because of the important safety roll these systems play, most manufacturers are going to great strides to ensure they are robust, with reliable components.

The body shop industry will likely see the biggest issues from these systems as they will need to be recalibrated if there is any damage done to the radar or other headway sensors.

A scan tool and proper service instructions are going to be vital to do any work on the system. But body shop techs aren’t going to be the only ones removing the front end components of many newer vehicles.


AC service, cooling service, and headlight replacement often require removal of the front bumper covers and grills in order for the tech to gain access. This will possibly involve recalibration.

The ACC system has become far more affordable and is now popular on lower- and medium- priced vehicles now, so there may be a need to supply parts to these vehicles as they age and as they require other services that involve disassembly.

When other vehicle systems, such as stability control and braking, require servicing, the ACC will typically be disabled, due to the interdependency of the systems. This, too, may affect parts and service opportunities.

Where is all of this going?

Mercedes Benz and Audi have the stop-and-go ACC that will steer the vehicle and keep it following the vehicle in front of it. The driver can even take their hands off the steering wheel (though it is not recommended) and the vehicle will pretty much be self-directed.

This vehicle is not yet autonomous though. If the driver’s hands are off the steering wheel for too long, a warning lamp will light up on the dash.

One of the best advantages of an ACC system is that it can give the driver that crucial split second of warning that they’re closing in on another vehicle too fast. That may be enough to prevent an accident.

The ACC system provides this safety buffer and that may be a welcomed feature these days with all the other distraction and fatigue that we as drivers are faced with during the average commute.


Jeff Taylor is a frequent contributor to CARS magazine. He is lead technician at Eccles Auto Service in Dundas, Ont., and a previous winner of both the Canadian Technician of the Year, and the ACDelco Technician of the Millennium.

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2 Comments » for Adapting to speed and distance
  1. Keg says:

    These articles are great. Is there any central area that has the links to all 7 articles? Or is there an easy way to access them all?

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